This invention relates to a method and apparatus for determining the operability of a moistening arrangement for applying moisture to the gummed flaps of envelopes or the like, especially for ensuring the proper moistening of gummed flaps in a high speed mailing machine.
U.S. Pat. No. 3,911,862 discloses a moistening system for envelope flaps wherein a pair of fixed nozzles are aligned to selectively spray water against an envelope flap, in dependence upon the output of a sensor arranged to detect the location of the edge of the flap in the plane perpendicular to the direction of motion of the envelope that passes through the nozzles. Thus, a first of the nozzles is controlled to spray water at the flap if the sensor does not detect the envelope flap, and the other of the nozzles sprays water if the sensor does detect the envelope. In this arrangement, another sensor is arranged to control the supply of water to the nozzles when the leading edge of the envelope passes a determined position, and to inhibit the supply of water to the nozzles when the trailing edge of the envelope has passed that position. In an alternative arrangement, instead of employing two (or more) nozzles, the reference discloses the movement of a single nozzle between two end positions by means of a solenoid, under the control of the output of the flap edge position sensor, or under the control of feedback from a contoured template.
The system disclosed in the above reference, however, is not adapted to the high speed moistening of envelopes, especially since consideration is not given to the rapid change of the position of the moistener nozzle required for high speed movement of the envelopes. In addition, the above system turns the spray from the nozzle on and off solely in response to the sensing of the leading and trailing edges of the envelope, independently of the configuration of the flap, and is not adapted to compensation for response times of various movable elements of the system or control of the moisture necessary for properly moistening the envelope flaps.